This assumption is based in part on long-term valuation analysis and in part on my two-and-a-half decades of market experience, during which I have learned many searing lessons about how markets behave.

As one reader was quick to point out, it is also "just a guess."

By pointing that out, the reader reminded me of a profoundly important point about investing, one that many casual observers often don't fully understand.

Every market outlook is "just a guess."

Every one.

Some guesses are more informed than others, of course. But no one knows the future. Everyone's just guessing.

As a stock analyst in the 1990s, I assumed for many years that somewhere there was someone who knew what the market was going to do.

Over the course of my career, I met ever more sophisticated and talented market players, including a handful of the most sophisticated investors and traders in the world.

All of these folks were brilliant, confident, persuasive, and astoundingly well informed. They had made billions of dollars in the market. They had decades of experience. They knew everything it was legal to know, and often considerably more.

And, as the future eventually made clear, not a single one of them knew what the market was going to do.

It wasn't until I realized this firsthand that I fully "got it."

No one knows what the market is going to do.

We're all "just guessing."

That realization was one of several that helped me develop the investing strategy I use today (indexing.) There is no question that this is the best strategy for me and almost every other investor. When you index, you save pots of money on fees and mistakes, the latter usually caused by the assumption that you or someone else knows what the market is going to do. And this pot of money that you save will help you achieve returns that are better than about 90% of other investors, especially after tax. And that's without any work or worry or heartache at all.

Even if you don't yet understand why indexing wins, however, please at least understand this: